Atrial fibrillation is one of the most common cardiac arrhythmia. Atrial fibrillation is a debilitating disease that afflicts 20 million people worldwide. Health consequences associated with atrial fibrillation include decreased cardiac output, less regular ventricular rhythm, the formation of blood clots in the atrial appendages, and an increased incidence of stroke. While some drugs are available for the treatment of atrial fibrillation, they have a number of side effects which reduce their therapeutic utility. The use of atrial counter shocks remain one of the primary treatments for atrial fibrillation.
Unlike patients afflicted with ventricular fibrillation, patients afflicted with atrial fibrillation are conscious. The pain associated with the administration of the defibrillation shock can be severe, and there is a need to reduce the pain to the patient being treated while maintaining clinical efficacy of the defibrillation shock. Internal, catheter-based atrial defibrillation has been found to increase efficacy while requiring lower shock strength in comparison to traditional transthoracic cardioversion. Implantable devices for internal catheter-based atrial defibrillation have been developed and are being clinically investigated. However, the clinical acceptance of implantable atrial defibrillation devices may be limited by the discomfort associated with the atrial defibrillation shocks. Other fibrillation-based treatments in which pain may be experienced by the patient include the treatmentment of hemodynamically stable ventricular tachycardia.
Furthermore, pain and discomfort are difficult to quantify in an absolute measurement. One method for estimating pain is to ask patients to rate the pain that they experience. This method depends on the subjectivity of the patient, and therefore, it is difficult to compare the assessment of pain reported from one patient with the assessment of pain reported from other patients. The difficulties and inaccuracies in measuring pain and discomfort complicate the problem of minimizing pain in various types of treatments, including atrial defibrillation.
Systems and methods proposed that deliver atrial defibrillation include U.S. Pat. No. 5,165,403 to R. Mehra (“Mehra”), the contents of which are hereby incorporated by reference as if recited in full herein. Mehra discloses an implantable lead system useful for defibrillating (or “cardioverting”) the atria of a patient's heart. In the disclosed system, one electrode is positioned in either the great cardiac vein or coronary sinus of the heart, and another electrode is positioned in either the right atrium or superior vena cava of the heart.
U.S. Pat. No. 6,327,500 to Cooper et al., the contents of which are hereby incorporated by reference as if recited in full herein, discloses an implantable system for defibrillation of the atria of a patient's heart. A pulse generator delivers a second atrial defibrillation pulse after a first defibrillation pulse without intervening monitoring thereof to reduce the voltage necessary for the shock.
U.S. Pat. Nos. 5,978,705 and 6,275,730, both to KenKnight et al., the contents of which are hereby incorporated by reference as if recited in full herein, each disclose an implantable system for the defibrillation or cardioversion of the heart comprising a plurality of primary electrodes, a power supply, and a control circuit. The primary electrodes are configured for delivering a cardiversion pulse along a predetermined current pathway in a first portion of the heart where the current pathway defines a weak field area in a second portion of the heart.
However, there remains a need for measuring and/or reducing the discomfort and pain associated with shocks for treating atrial fibrillation, hemodynamically stable ventricular tachycardia, and other conditions in which discomfort and pain may be problematic.